Surgical implants can include mechanisms that require external manipulation during or after implantation. For example, an implant can include anchoring elements, locking elements, position-adjusting elements, or other types of elements or features that allow the implant to operate in a manner to promote healing and/or stabilization of the anatomy of the patient. One example of such an implant includes an intramedullary nail implanted within a medullary cavity of a long bone, such as a femur, for example, to stabilize a fracture in the bone. It has been common practice to affix the intramedullary nail with respect to the bone by placing locking members, such as screws, through access holes drilled through at least a cortex of the bone and in alignment with anchoring holes, such as threaded bores, that are pre-drilled transversely in the nail. The procedure presents technical difficulties, as the pre-drilled bores in the intramedullary nail are not generally visible to the surgeon, and are difficult to localize and to align with surgical drills and placement instruments for drilling the access holes in the bone and/or inserting the locking members.
Distal targeting systems are used in many instances to detect the location of various elements of an implant during a surgical procedure. With respect to the foregoing intramedullary nail example, a distal targeting system can be employed with the surgical drill to locate the position of the one or more anchoring bores in the intramedullary nail and provide feedback to the physician indicating the relative positions of the anchoring bores with respect to a distal end of a drill bit of the surgical drill. Such distal targeting systems can include a magnetic field generator (also referred to as simply a “field generator”) having a central guide bore in which the drill bit is received. The field generator includes circuitry for generating one or more magnetic fields. The intramedullary nail can include one or more sensors each having one or more field transponders configured to detect the direction and strength of the magnetic fields generated by the field generator. The one or more sensors can each transmit magnetic field data to a control unit having control circuitry. The one or more sensors can be located with respect to the intramedullary nail so that the relative positions of the one or more sensors and the one or more anchoring bores are known by the control unit. The orientation and position of a central axis of the guide bore are also known by the control unit. The central axis of the guide bore approximates a central axis of a drill bit received within the guide bore.
The control unit interprets the data from the one or more sensors to ascertain the orientation and displacement of the central axis of the guide bore relative to the one or more anchoring bores in the intramedullary nail. The control unit transmits feedback to the physician, such as visual feedback via a view screen or audio feedback via a speaker, indicating the orientation and/or displacement of the central axis in relation to the anchoring bores in the intramedullary nail. Distal targeting systems for use with other types of surgical implants can employ similar structures and techniques.